1. Field of the Invention
The present invention generally relates to oscillators, and more particularly, to an oscillator suitable for radio-frequency (RF) circuits.
2. Description of the Related Art
Conventionally, various types of oscillators such as a local oscillator for FM tuners, a crystal oscillator, and a voltage-controlled oscillator are used. A Colpittz oscillator and a Hartley oscillator are known as LC oscillators. The LC oscillator employs a resonant circuit by the combination of an inductor L and a capacitor C. The LC resonant circuit is capable of generating an oscillation signal over a wide frequency range. Generally, a buffer circuit follows the LC oscillation circuit of the oscillator in order to stabilize oscillation.
Recently, there has been considerable activity in the development of downsized oscillator due to downsizing of electronic devices. However, the oscillator composed of the oscillation circuit and the buffer circuit has reached the limit of downsizing.
FIG. 1 is a circuit diagram of a conventional Colpittz oscillation circuit. The Colpittz oscillator circuit is made up of a transistor TR, capacitors C1 and C2, resistors R1, R2 and R3 and an inductor L. A power supply voltage is applied to the oscillator via a terminal P1. A series circuit of the resistors R1 and R2 is connected between the terminal P1 and ground, and generates a DC bias voltage, which is applied to the base of the transistor TR. The emitter is biased by the resistor R3 that serves as an emitter bias resistor. A buffer circuit (not shown) follows the Colpittz oscillation circuit. More particularly, the buffer circuit is connected to the emitter of the transistor TR.
However, the conventional oscillator composed of the oscillation circuit and the buffer circuit has a disadvantage in that the oscillation signal is not extracted efficiently.